1. Field of the Invention
The present invention relates to a reproducing and recording apparatus, a decoding apparatus, a recording apparatus, a reproducing and recording method, a decoding method and a recording method in which acoustic characteristics of compressed digital data are changed by effecting calculation on normalized information in the compressed digital data.
2. Description of the Related Art
Heretofore, there have been a variety of audio signal high-efficiency coding methods and apparatus, and a few examples of such audio signal high-efficiency coding methods and apparatus will be described below. There is known a method called a transform coding method which is one of block frequency-band division systems in which an audio signal of a time region is blocked at every unit time, a signal of a time axis of every block is transformed into a signal on a frequency axis, i.e. quadrature-transformed and then coded at every band. Also, there is known a method called an SBC (Sub Band Coding) method which is one of non-block frequency band division methods in which an audio signal of time region is not blocked at every time unit but divided into a plurality of frequency bands thereby coded. Further, there is known a high-efficiency coding method which is a combination of the above-mentioned band division coding method and the transform coding method. In that case, after the band is divided by the above-mentioned band division coding system, the signal of every band is quadrature-transformed into a signal of a frequency region by the above-mentioned transform coding system, and the coding is effected at very orthogonal-transformed band.
As a band-division filter used in the above-mentioned band division coding system, there is known a filter such as QMF (Quadrature Mirror filter). This QMF is described in 1976 E. E. Crochiere Digital coding speed in subbands Bell Syst. Tech. J. Vol. 55, No. 8. 1976. Also, ICASSP 83, BOSTON Polyphase Quadrature filtersxe2x80x94A new subband coding technique Joseph H. Rothweiler describes equal band width filter dividing method and apparatus such as PQF (Polyphase Quadrature filter).
Also, as the above-mentioned quadrature transform, there is known a quadrature transform in which an input audio signal is blocked at a predetermined unit time (frame) and the time axis is transformed into the frequency axis by effecting FFT (Fast Fourier Transform) or DCT (Discrete Cosine Transform) or MDCT (Modified Discrete Cosine Transform). The above-mentioned MDCT is described in ICASSP 1098 Subband/Transform Coding Using Filter Bank Designs Based on Time Domain Aliasing Cancellation J. P. Princen A. B. Bradley Univ. of Surrey Royal Melbourne Inst. of Tech.
Further, as a frequency dividing width used when each frequency-band-divided frequency component is quantized, there is known a band division considering man""s auditory characteristics. That is, in a band width in which the band width is widened in the high band on the frequency axis called a critical band, an audio signal is divided into a plurality of bands, e.g. 25 bands. When data of every band of this time is encoded, the encoding is executed by a predetermined bit distribution of every band or adaptive bit distribution of every band. For example, when MDCT coefficient data of every band obtained by the MDCT processing is encoded by the bit distribution, the encoding is executed by the adaptive distribution bit number.
Further, in the case of the encoding at every band, data is normalized at every band and quantized, thereby effecting a so-called block floating processing in which a more efficient encoding can be realized. For example, when the MDCT coefficient data obtained by the above-mentioned MDCT processing is encoded, data is normalized in response to the maximum value of the absolute value of the above-mentioned MDCT coefficient at every band and quantized, thereby making it possible to execute the more efficient encoding. In the normalization, there are in advance determined a plurality of numbers corresponding to size information, and the numbers are used as normalization information. The size information of the previously-determined normalization is numbered at an interval of a constant magnitude.
As the bit distribution method and apparatus therefor, there have been heretofore known the following two methods.
In the IEEE Transactions of Acoustics, Speech, and Signal Processing, vol. ASSP-25, No. 4, August 1977, bits are distributed on the basis of the magnitude of the signal of every band. Further, in the ICASSP 1980 The critical band coder-digital encoding of the perceptual requirements of the auditory system M.A. Kransner MIT, there is described a method in which a signal-to-noise ratio necessary for every band is obtained by using an auditory masking and bits are distributed in a fixed fashion.
A signal high-efficiency coded by the above-mentioned method is decoded by the method which follows. Initially, the high-efficiency coded signal is calculated as MDCT coefficient data by using bit distribution information of every band, normalization information or the like. The MDCT coefficient data is transformed into data of time region by so-called IMDCT. When data is band-divided by the band-dividing filter upon encoding, data are further synthesized by using a band-synthesizing filter. By the above-mentioned operation, data of the original time region is decoded.
With respect to the signal of the time region which results from decoding the high-efficiency coded signal, let it be considered that the magnitude of the amplitude, i.e. reproduction level is adjusted and that a filter processing which is the level adjustment of every band is executed. When the reproduction level is adjusted, such adjustment is realized by effecting multiplication, addition or subtraction of a constant amount of the signal component of the time region which is not yet encoded fundamentally or the signal component which is decoded to the time region. Further, when the filter processing is executed, such filter processing is realized by a so-called convolutional computation or a combination of delay circuits and multipliers. In both cases, there are required a plurality of multipliers, adders, delay circuits and the like so that the processing process increases.
Also, there is considered a method in which the reproduction level is adjusted by MDCT coefficient data of the MDCT frequency region and the filter is realized by further adjusting the level. With respect to this method, there are required multipliers or adders or multiplication using the subtracter or addition or subtraction of the number corresponding to the number of the MDCT coefficient data so that the processing process increases.
Further, a similar problem arises when the high-efficiency coded signal is recorded on a certain recording medium and the signal of the time region in which the recorded signal is decoded is re-recorded in such a manner that information is changed such that the magnitude of the amplitude, i.e. reproduction level is changed or when information is re-recorded under the condition that information is changed in the form of being processed by the so-called filter effect. In particular, when the reproduction level is adjusted in the time region and the adjusted result is re-recorded on the recording medium, the IMDCT and the MDCT should be executed so that a quality is deteriorated by computation error or the like.
A similar problem arises when a filter processing is realized by the transform to the analog region.
When an analog audio signal is processed by filter processing such as a low-pass filter, a buzz-boost filter, a bandpass filter, a high-pass filter or the like, so-called effect processing, there has heretofore been required a special processing IC.
Also, in order to effect the filter processing on a part of audio signal, after a high-efficiency coded digital audio signal is expanded and a part of the expanded audio signal is processed by a filter processing, a resultant audio signal cannot be high-efficiency coded.
In view of the aforesaid aspect, it is a first object of the present invention to provide a reproducing and recording apparatus, a decoding apparatus, a recording apparatus, a reproducing and recording method, a decoding method and a recording method in which an adjustment of reproduction level of a signal of a time region in which a high-efficiency coded signal is decoded can be realized by smaller processing process.
It is a second object of the present invention to provide a reproducing and recording apparatus, a decoding apparatus, a recording apparatus, a reproducing and recording method, a decoding method and a recording method in which a signal of a time region in which a high-efficiency coded signal is recorded on a certain recording medium and the recorded signal is decoded can be re-recorded by smaller processing process while the reproduction level is changed and a quality can be prevented from being deteriorated when a computation such as IMDCT and MDCT is executed.
It is a third object of the present invention to provide a reproducing and recording apparatus, a decoding apparatus, a recording apparatus, a reproducing and recording method, a decoding method and a recording method in which a filter processing on a signal of a time region in which a high-efficiency coded signal is decoded can be realized by smaller processing process and simple arrangement and in which a filter processing of an arbitrary portion with respect to the time region signal becomes possible.
It is a fourth object of the present invention to provide a reproducing and recording apparatus, a decoding apparatus, a recording apparatus, a reproducing and recording method, a decoding method and a recording method in which a signal of a time region in which a high-efficiency coded signal is recorded on a certain recording medium and the recorded signal is decoded can be re-recorded by smaller processing process and simple arrangement while information is changed in the form of information with a filter effect achieved thereon, a filter processing of an arbitrary portion with respect to the time region signal becomes possible and in which a quality can be prevented from being deteriorated when a computation such as IMDCT and MDCT is executed.
According to an aspect of the present invention, there is provided a reproducing and recording apparatus which is comprised of data read means for reading compressed digital data including spectrum data whose band is divided into a plurality of bands on a frequency axis and a scale factor of every divided band from a recording medium, computation means for receiving compressed digital data including the band-divided spectrum data and the scale factor of every divided band from the data read means and effecting a computation for changing acoustic characteristics of the compressed digital data, and recording means for re-recording the compressed digital data whose acoustic characteristics are changed when the computation means computes the scale factor of the every band on the recording medium.
According to another aspect of the present invention, there is provided a decoding apparatus which is comprised of computation means for receiving compressed digital data including spectrum data which is band-divided into a plurality of bands on a frequency axis and a scale factor of every divided band and effecting a predetermined computation on the scale factor of the every divided band, normalization means for normalizing the band-divided spectrum data contained in the compressed digital data based on the scale factor of the every divided band computed by the computation means, IMDCT means for obtaining band-divided digital data on a time axis by processing the band-divided spectrum data normalized by the normalization means in an IMDCT fashion, and band-synthesizing means for band-synthesizing the digital data on the time axis band-divided by the IMDCT means.
According to other aspect of the present invention, there is provided a recording apparatus which is comprised of MDCT means for processing an inputted digital signal on a time axis in a MDCT fashion to provide spectrum data on a frequency axis, scale factor calculating means for calculating a scale factor of every divided band for normalization by band-dividing the spectrum data on the frequency axis, data compressing means for providing compressed data including a scale factor of every divided band and spectrum data by compressing the spectrum data on the frequency axis calculated by the scale factor calculating means, computation means for receiving compressed digital data including the scale factor of the every divided band and spectrum data from the data compressing means and effecting a computation for changing acoustic characteristics of the compressed digital data on the scale factor of the every divided band, and recording means for recording the compressed digital data in which acoustic characteristics are changed when the computation means computes the scale factor of the every band on a recording medium.
According to a further aspect of the present invention, there is provided a reproducing and recording method which comprises the steps of reading compressed digital data including spectrum data on a frequency axis band-divided and a scale factor of every divided band from a recording medium, effecting a computation for changing acoustic characteristics of the compressed digital data on the scale factor of the every divided band in compressed digital data including the read out spectrum data on the frequency axis band-divided and the scale factor of every divided band, and re-recording the compressed digital data whose acoustic characteristics are changed on the recording medium by computing the scale factor of the every band.
According to yet a further aspect of the present invention, there is provided a decoding method which comprises the steps of effecting a predetermined computation on the scale factor of every divided band in compressed digital data including spectrum data on a frequency axis band-divided into a plurality of bands and the scale factor of every divided band, normalizing the band-divided spectrum data in the compressed digital data based on the computed scale factor of the every divided band, providing digital data on a time axis band-divided by processing the normalized band-divided spectrum data in an IMDCT fashion, and band-synthesizing digital data on the time axis band-divided.
In accordance with still a further aspect of the present invention, there is provided a recording method which comprises the steps of transforming an inputted digital signal on a time axis into spectrum data on a frequency axis in an MDCT fashion, calculating a scale factor of every divided band for normalization by band-dividing spectrum data on the frequency axis into a plurality of bands, providing compressed digital data including a scale factor of every divided band and spectrum data by compressing the band-divided spectrum data on the frequency axis in response to the calculated scale factor of every divided band, receiving compressed digital data including the scale factor of the every divided band and spectrum data and effecting a computation for changing acoustic characteristics of the compressed digital data on the scale factor of the every divided band, and recording the compressed digital data whose acoustic characteristics are changed on a recording medium by computing the scale factor of the every band.